logo elektroda
logo elektroda
X
logo elektroda
Advanced Search
logo elektroda

[Solved] Choosing a Fuse for 10kW Heater with 400V Power Supply: Understanding Phase Currents

wiesko42 21069 16
Best answers

How do I choose fuses for a 10 kW heater on a 400 V three-phase supply, and is the 25 A current per phase or for the whole system?

If the heater is star-connected, the current is about 14.5 A per phase/branch, not 25 A for the whole system [#17938421][#17938796] The 10,000/400 calculation is not the right way to size a three-phase resistive heater; in a star connection you calculate the branch current from the 230 V per heater and assume cos φ = 1 [#17935781][#17938421] One reply suggested 20 A protection, while another said 16 A per phase is reasonable, but you must also consider that a cold heater draws more current at switch-on than a hot one [#17935702][#17935861] If the wiring were delta, the phase current would be different, so confirm the actual connection or measure one heater’s resistance [#17938796]
Generated by the language model.
ADVERTISEMENT
Treść została przetłumaczona polish » english Zobacz oryginalną wersję tematu
Report a violation of the law
| New topic
  • #1 17935525
    wiesko42
    Level 8  
    Posts: 83
    Rate: 24
    Hello
    I need help selecting fuses for the heater.
    10kW heater, 400V power supply
    And so P=UxI | I=P/U | I=10000/400=25A
    And now I don't know whether 25A is the sum for the entire line (3x8.33A) or for a single phase?

    The second thing is that the heater consists of 3 heaters connected in a star pattern, which means that one heater has 3333W and a voltage of 230V, and as above
    I=3333W/230V=14.5A but with a 230V power supply and the entire system is 400V
    Maybe someone will help you choose.
  • ADVERTISEMENT
  • #2 17935555
    kortyleski
    Level 43  
    Posts: 12262
    Help: 957
    Rate: 3833
    What type of heater is it? Because something about these powers doesn't suit me. Generally, you calculate the current for one star branch at a specific power and voltage of 230V. At the same time, it is a good idea to connect the center point of the star with N. During normal operation, it does not matter, but if one heater fails, the other two work normally.
  • ADVERTISEMENT
  • #3 17935562
    Pyzaczek
    Level 20  
    Posts: 1013
    Help: 37
    Rate: 107
    wiesko42 wrote:
    I need help selecting fuses for the heater.

    wiesko42 wrote:
    ...the heater consists of 3 heaters connected in a star pattern, hence it may result that one heater has 3333W and a voltage of 230V and as above
    I=3333W/230V=14.5A...

    No help needed, calculations OK
  • #4 17935673
    wiesko42
    Level 8  
    Posts: 83
    Rate: 24
    Ok, so 16A protection per phase. But then what current will be consumed by this heater system? 25A or maybe 14.5 x3 = 43.5A I don't understand here?
  • #5 17935702
    Pyzaczek
    Level 20  
    Posts: 1013
    Help: 37
    Rate: 107
    I would give 20 A. Consumption 14.5 A from each phase.
  • Helpful post
    #6 17935781
    retrofood
    VIP Meritorious for electroda.pl  
    Posts: 31317
    Help: 1140
    Rate: 4781
    wiesko42 wrote:
    Ok, so 16A protection per phase. But then what current will be consumed by this heater system? 25A or maybe 14.5 x3 = 43.5A I don't understand here?

    Play around with this:
    Power and current calculator in three-phase systems

    Use cos φ = 1, If - current of one phase
  • ADVERTISEMENT
  • #7 17935861
    nuszek
    Level 30  
    Posts: 1421
    Help: 123
    Rate: 388
    14.5 A for each phase, but it should be noted that the power is given for a heated heater, when a cold heater is switched on, its resistance is lower and the current will be higher when switched on, and this must be taken into account when selecting the protection.
  • #8 17938395
    wiesko42
    Level 8  
    Posts: 83
    Rate: 24
    The view and available description are attached.
    I didn't expect that the current consumed by the heater would be so high 14.5x3=43.5A I don't understand now since the heater is powered by 400V then P=400Vx43.5A| P=17.4kW, not 10kW. I thought that the current would be of the order P=UxI| I= 10000W/400V| I=25A, I will not mention the calculations from the calculator provided in the thread where the value is 18A.
    Attachments:
    • Choosing a Fuse for 10kW Heater with 400V Power Supply: Understanding Phase Currents widok grzałki.jpg (28.77 KB) You must be logged in to download this attachment.
    • Choosing a Fuse for 10kW Heater with 400V Power Supply: Understanding Phase Currents opis grzałki.jpg (138.84 KB) You must be logged in to download this attachment.
  • #9 17938421
    kortyleski
    Level 43  
    Posts: 12262
    Help: 957
    Rate: 3833
    The description is misleading. The heater is connected in a star, so the power supply for each branch of the star is 230V. And for this voltage you calculate the branch current. So 3300/230.
  • #10 17938533
    wiesko42
    Level 8  
    Posts: 83
    Rate: 24
    Ok, at this point I may have misled the forum users. The description of the product I bought does not indicate that it is star-connected. I cannot contact the distributor. When I have more information, I will post it here. Thank you for your help
  • #11 17938592
    kortyleski
    Level 43  
    Posts: 12262
    Help: 957
    Rate: 3833
    Show me what the connection looks like under this white box.
  • #12 17938796
    Pyzaczek
    Level 20  
    Posts: 1013
    Help: 37
    Rate: 107
    If the heaters are connected in a star, the current consumption from each phase is 14.5 A, and if they are connected in a delta, the current consumption from each phase is approximately 8 A.
    That's what.
    Measure the resistance of one heater and everything will be clear.
  • ADVERTISEMENT
  • #13 17938863
    nuszek
    Level 30  
    Posts: 1421
    Help: 123
    Rate: 388
    Pyzaczek wrote:
    If the heaters are connected in a star, the current consumption from each phase is 14.5 A, and if they are connected in a delta, the current consumption from each phase is approximately 8 A.
    That's what.

    What nonsense , 10 kW in a star is also 10 kW in a triangle, the current on each phase will be the same, i.e. 14.5 A.
    Approx. 8 And it will flow when two heaters burn out and only one of the triangle connections remains.
  • #14 17938886
    retrofood
    VIP Meritorious for electroda.pl  
    Posts: 31317
    Help: 1140
    Rate: 4781
    nuszek wrote:
    Pyzaczek wrote:
    If the heaters are connected in a star, the current consumption from each phase is 14.5 A, and if they are connected in a delta, the current consumption from each phase is approximately 8 A.
    That's what.

    What nonsense , 10 kW in a star is also 10 kW in a triangle, the current on each phase will be the same, i.e. 14.5 A.
    Approx. 8 And it will flow when two heaters burn out and only one of the triangle connections remains.

    If you guys used the right terms, there would be no disputes. In a star, phase current = current of 1 heater, but in a triangle the phase current is different from the current of 1 heater.
  • #15 17938995
    wiesko42
    Level 8  
    Posts: 83
    Rate: 24
    Resistance +/- 17.5 Ohm for one heater. The connection shows that it is a star. I don't understand why the markings are 3x400V and not 3x230V? As I understand it, from common N, each heater is connected to a single phase. G1-f1, G2-f2, G3-f3, so there is 230V per heater.

    Unless the heater is simply for 400V phase voltage and interphase voltage is 690V
    Attachments:
    • Choosing a Fuse for 10kW Heater with 400V Power Supply: Understanding Phase Currents IMG-5454.jpg (430.58 KB) You must be logged in to download this attachment.
    • Choosing a Fuse for 10kW Heater with 400V Power Supply: Understanding Phase Currents IMG-5453.jpg (397.81 KB) You must be logged in to download this attachment.
  • #16 17939038
    retrofood
    VIP Meritorious for electroda.pl  
    Posts: 31317
    Help: 1140
    Rate: 4781
    You have a clear star like a bull. Without a doubt.
  • #17 17946442
    wiesko42
    Level 8  
    Posts: 83
    Rate: 24
    The 3x400V marking is the manufacturer's marking. I still don't understand this marking for star connection. In any case, the heater is powered by 3X230V. The rest is as in the posts above. Greetings to forum members. Current flowing 3x 14.5A
| New topic
Report a violation of the law

Topic summary

✨ The discussion revolves around selecting appropriate fuses for a 10kW heater powered by a 400V supply. The user calculates the current as 25A for the entire system but is confused about whether this is the total or per phase. The heater consists of three units connected in a star configuration, leading to a phase current of approximately 14.5A per heater at 230V. Participants clarify that the current consumption from each phase is indeed 14.5A, and suggest using 16A or 20A fuses for protection, considering the inrush current when the heater is cold. The conversation highlights the importance of understanding the connection type (star vs. delta) and the implications for current calculations. The user later confirms the star connection and expresses confusion over the manufacturer's 3x400V marking, which is clarified as being standard for such configurations.
Generated by the language model.

FAQ

TL;DR: For a 10 kW, 400 V star‑connected heater, each phase draws 14.5 A; "14.5 A from each phase." Choose 20 A per‑phase fuses. [Elektroda, Pyzaczek, post #17935702]

Why it matters: For electricians, techs, and DIYers who need to size fuses and understand phase currents on three‑phase heaters fast.

Quick Facts

How do I calculate phase current for a 10 kW three‑phase heater on 400 V?

For a star heater with three equal elements, use per‑branch values. Each element is about 3.33 kW at 230 V. The current per phase equals branch current for star. I_phase = P_branch / 230 V ≈ 14.5 A. That matches the thread’s confirmed result. [Elektroda, Pyzaczek, post #17935702]

Is the 25 A from 10000/400 the total line current?

That 25 A comes from a single‑phase formula, so it misleads here. In a 400/230 V star, calculate using 230 V per branch. Each phase then carries about 14.5 A. Do not add phase currents together. [Elektroda, kortyleski, post #17938421]

What fuse size should I use per phase for this heater?

The thread recommends 20 A per‑phase protection for a 14.5 A branch current. This gives working margin without nuisance trips. Confirm device curve and ambient limits with your protection hardware’s datasheet. [Elektroda, Pyzaczek, post #17935702]

Why should I connect the neutral to the star point?

Connecting N to the star point stabilizes voltages during a failure. If one element opens, the other two still see 230 V. Without N, unbalance can over‑ or under‑voltage the remaining elements. It is a simple reliability gain. [Elektroda, kortyleski, post #17935555]

How do star and delta wiring change phase and branch currents?

In star, the line current equals the current of one heater element. In delta, the line current differs from the element current. As one expert put it, “In a star, phase current = current of 1 heater.” Use correct terms to avoid errors. [Elektroda, retrofood, post #17938886]

How can I verify whether my heater is wired in star or delta?

Kill power and open the terminal box. Look for three element ends tied together; that is the star point. Measure one element’s resistance to confirm continuity and estimate current. Then match the nameplate and compute branch current at 230 V.
  1. Isolate power and lock out.
  2. Open the box; check for a tied star point.
  3. Measure element resistance; compute I = 230 V / R. [Elektroda, Pyzaczek, post #17938796]

Why does the nameplate say 3×400 V if each element is 230 V?

Manufacturers often mark the supply system rather than element voltage. In a 400/230 V system, star‑connected elements each see 230 V. The OP confirmed this: “the heater is powered by 3×230V.” The 3×400 V label denotes the three‑phase supply. [Elektroda, wiesko42, post #17946442]

What current does the whole 10 kW heater draw from the mains?

Expect about 14.5 A in each of the three phases. Do not multiply by three for total current. Size upstream protection based on the per‑phase current and device characteristics. [Elektroda, Pyzaczek, post #17935702]

Is there a calculator I can use, and what settings?

Yes. Use a three‑phase power–current calculator and set cos φ = 1. Read If as the current of one phase. The PRS calculator linked in the thread is suitable. “Use cos φ = 1, If – current of one phase.” [Elektroda, retrofood, post #17935781]

What happens at switch‑on with cold heater elements?

Cold elements have lower resistance, so inrush current exceeds the steady 14.5 A. Select protection with headroom to ride through this transient. This avoids nuisance tripping at startup. [Elektroda, nuszek, post #17935861]

What resistance did users measure on a single heater element?

One measurement reported approximately 17.5 Ω for a single element. That reading came from a heater confirmed as star‑connected. Use your multimeter to verify your unit. Differences reflect tolerance and temperature during measurement. [Elektroda, wiesko42, post #17938995]

If one element burns out, will the other two still work?

With the neutral tied to the star point, the other two keep normal operation. Without neutral, voltages can shift and stress the remaining elements. Connecting N is a simple reliability improvement. [Elektroda, kortyleski, post #17935555]

Is phase current about 8 A if the heater is delta‑connected?

No. That figure is incorrect for a 10 kW three‑phase heater. In delta, the relation between line and element currents differs from star. Use correct definitions before calculating currents. [Elektroda, retrofood, post #17938886]
Generated by the language model.
ADVERTISEMENT